Electrical contact means



May 7, l1940.

J. SLEPIAN ELEGTRIQAIL CONTACT MEANS 'Filed April 14, 1938 WITNESSES:

(Patented May 7, 1940 PATENT OFFICE ELECTRICAL CONTACT MEANS JosephSlepian, Pittsburgh, Pa., assignor to West- .inghouse Electric &Manufacturing Company, East Pittsburgh, Pa., a corporation of Penn-Sylvania Application April 14, 1938, Serial No. 202,016

22 Claims. (Cl. 200-149) The invention relates to electrical contactmeans for switches and circuit breakers that are adapted to interrupt acircuit under load and overload conditions. v

Prior to the present invention it has been the usual practice to providecircuit breakers with some form of arc extinguishing means or-device for'extinguishing the arcs formed during circuit interruption. This Wasfound necessary in order to shorten the time required for completecircuit interruption and to protect the contacts from damage by thearcs.

An object of the invention is the provision of electrical contactsthatare capable of extinguishing the arcs formed during circuitinterruption.

Another object ofthe invention is the provision of electrical contactscontaining an appreciable quantity of a substance which gives off an arcextinguishing gas or vapor when acted on by an arc for quicklyextinguishing the arc.

Another objectof the invention is the provision of an electrical contactas previously described in which the arc extinguishing substance issubstantially uniformly distributed through the conduct- '25 ingmaterial of the contacts. ,y

The contact means of the present invention may be used without anyadditional or separate arc extinguishing device, or they may be used inconjunction with an arc extinguishing device to materially aid the samein more quickly exhowever, both as to'structure and operation, to'

gether with additional objects and advantages thereof, will best beunderstood from the following detailed description of severalembodiments thereof when considered in connection with the y40accompanying drawing, in which:

Figure 1 is a v ertical sectional view of a contact means constructed inaccordance with the invention,

Fig. 2 is a sectional view of a modified form of contact, and

Fig. 3 is a sectional view of another modified form of contact.

Referring to Figure 1 of the drawing, the reference numerals I and 2indicate a p'air of coaxially `mounted separable contacts of a circuitbreaker or other form of 'circuit interrupting device. The contact I iscarried by a rigid support 3 to form thr stationary Contact, and thecontact 2 is movable into and out of engagement with the stationi- 5lary contact I by any suitable form of circuit breaker operatingmechanism to establish and interrupt an electrical vcrcuit in which thecontacts are connected.

.The stationary contact I is formed of wholly porous conducting materialsuch as copper or a l suitable alloy of -copper and other conductingmaterials, and is immersed to the level indicated in a body of arcextinguishing liquid such as oil, Water or the like held in a container4. The contact I may be made porous in any suitable manner l0 as, forexample, by thoroughly mixing a quantity of nely divided particles ofthe conducting material with an organic binder material such as soap,compressing the mixture into a composite mass of the desired shape, andheat treating the mass 15 to volatilize the soap and bond the conductingmaterial. The voids produced by the removal of the soap form asponge-like matrix which is about 60% to 70% solid and has a largenumber of small voids or passages which are substantially 20 uniformlydstributed and extend continuously through the matrix of conductingmaterial. The voids or passages in the contact are maintained I'llledwith the arc extinguishing liquid by capilv lary action of the smallvoids, and the contact is 25 preferably surrounded by a barrier 5 of asuitable porous insulating material which is partially submerged in theliquid so as to be soaked with the arc extinguishing liquid. The movablecontact 2 may be of Asolid conducting material, or of the 30 same porousmetal construction as the contact I and its voids impregnated with anarc extinguishing liquid by vacuum impregnation.

When the contacts I and 2 are connected in an electrical circuit landthe movable contact 35 moved to open circuit position to interrupt thcircuit under load or overload conditions, the heat of the arc drawnbetween the contacts liberates a considerable quantity of arcextinguishing gas or vapor from the arc extinguishing liquidA con- 40tained in the stationary contact I and also from the surrounding wallsof the barrier 5.

The arc extinguishing gas quickly extinguishes the arc in a well knownmanner. The evolution of the gas in the case of an alternating currentcon- 45 tinues as the current passes through its zero value introducingan unionized layer of gas as indicated by the dotted lines 6 in Fig. 1.'I'he thickness of the layer may be expected to grow at the rate ofabout l04 centimeters per second and its dielectric 59 strength may beabout 104` volts per centimeter.

Therefore, it should be capable of developing dielectricstrength at therate of about 10 volts per second. Since even the highest practical highvoltage circuits can develop voltage at only a few times this rate,several pairs of the contacts connected in series and provided withmeans for properly dividing the voltage therebetween should be able tosuccessfully interrupt even very high voltage circuits.

The barrier il in addition to increasing the quantity of arcextinguishing gas given oif also keeps the arc on the contact face ofthe stationary contact i. If desired, the barrier may be formed of amaterial such as horn fibre which gives ofi an arc extinguishing gaswhen acted on by an arc.

A number of tests have been made using porous metal contacts which werevacuum impregnated with oil in accordance with the present invention.

The oil impregnated porous copper contacts used were about 1/8 thiol:and 1%2" in diameter and each was surrounded by an annular ring orbarrier or" horn nbre for the purpose of keeping the arc on the `facesof the contact. The pair of contacts were mounted coaxially, the arcbeing drawn by separating the contacts a distance of /g. fdl the testswere made in the air. The results of the tests were as follows:

Cilrcuit M S Arc1 tim? vo tage cyc es o M. d. ampws cycle circuit Theabove results indicate that a singlepair of oil impregnated porous metalcontacts is capable of handling voltages up to about 350 to 400 volts R.M. S. over the wide range of currents tested.

A modified form of are extinguishing Contact is shown in Fig. 2.Referring to Fig. 2, the contact 7 consists of a mixture of silver andboric acid, the boric acid being in the form of powdered ortho-boricacid which is substantially uniformly distributed through the silver.rThe contact "l is formed by intimately mixing finely divided silver andpowdered ortho-1boric acid and afterwards compressing the mixture to thedesired shape in cause a rapid extinction of the arc in the case of lowvoltage circuits.

'I'he percentage by weight of the silver and boric acid of the contactmay be varied over a considerable range. The silver content may rangefrom about 50% to 90% by weight, and the boric acid content from about10% to 50% by weight, depending upon the particular operatingrequirements of the contacts. The circuit interrupting ability of thecontact improves as the boric acid content is increased. On the otherhand, the current carrying capacity decreases when the boric acidcontent is increased. A practical contact would, therefore,` have toweigh these two conilicting factors so as to obtain a material which notonly has the requisite circuit interrupting ability but which also has asatisfactory current carrying capacity. A contact which has been foundto give good all around performance is one containing about 80% byweight of silver and 20% by weight of boric acid where the object is toclear circuits having a voltage of the order oi volts.

A number of tests have been made using contacts composed of silver andboric acid having different percentages of the two materials. Thediameter of the contacts was about of an inch and each was surrounded byan annular barrier of horn bre to keep the arc on the face of thecontact. The contacts were separated 14 of an inch and the full contactseparation was obtained in about 1/60 of a second. The results of thesetests were as follows:

.il C. test date um Circuit Tillne to T' composition erccnt by weight)vo ts, c enr 1p (p pms D. C circuit Sccomc 2 80 A -20 boric acid- 310110 l %D g 110 .017 75% .Ag-25% boric aci 50 110 .Oli 06.7% Ag-33.3%boric acid 255 ll0 .013 50% ig-50% boric acid 38 260 .0i

A. C. test data-110 11.450 cycles R. M. S Time to clear Tlp compositionumpetes Circuit 90% .lig-10% boric acid 2, 220 K1 cycle. 80% Agg-20%boric acid Over 2,000 Probably $6 cycle. 66.7% fig-33.3% boric acid.. l,0 M cycle. 60% lig-40% boric acid Over 2,000 Probably cycle.

Another modified iorm of contact is illustrated in Fig 3, where thecontact 0 consists of a mixture of graphite and powdered boric acid, theboric acid being substantially uniformly distributed through thegraphite. The contact is formeel substantially in the same manner as theprevi ously described silver boric acid contact. fl quantity of i'lnelydivided particles of graphite are intimately mixed with powderedortho-boric acid. The mixture is compressed to a solid composite mass ofthe desired shape in suitable molds at a high pressure of severalthousand poiuids per square inch. Where the contact contains more thanabout 60% of graphite by Weight, the mixed powder is heat treated at amoderate temperature of from about 80 C. to 100 C. so that when theheated powder is compressed, a better bonding of .the materials willtake place.

When a pair of graphite boric acid contacts constructed as previouslydescribed are separated to interrupt an electrical circuit, the arcdrawn between the contacts causes the emission of water vapor from theboric acid immediately upon sep arating of the contacts. The water vaporraises the arc voltage a considerable amount to cause a rapid extinctionof the arc on low voltage circuits. 'I'he percentage by Weight of thegraphite and boric acid of the contact may be varied over a considerablerange. The circuit interrupting ability of the contacts increases as theboric acid content is increased. On the other hand, the current carryingcapacity of the contact is dccreased when the boric acid content isincreased. A practical 4content would, therefore, have to Weigh thesetwo conicting factors so as to obtain a contact which has the requisitecircuit interrupting ability but which also has a satisfactory currentcarrying capacity. A contact which is lil fifi

capable of giving good-all around results is one `which contains from50% to 60% by weight of graphite and the, remainder substantially all of'tacts composed of graphite and boric acid having different percentagesof the two materials. The diameter of the contacts was A, and each wassurrounded by an annular nbre barrier to keep the arc on the face of thecontact.. The contacts were separated 1A", and the full contactseparation was obtained in Vm of a second.

The results of the tests were as follows:

D. C. test data Circuit Time` to Tip composition Am- (percent by weight)peres Bls Seconds ampir-seiewcs-- a gra teo c ac anni) 53 26o .013 Do 96520 0l7 D0 810 520 .013

The invention in each of its several forms provides a simple 'andinexpensive contact means which is capable of quickly extinguishing anarc drawn between the contacts during circuit interruption under load oroverload conditions.

While the invention has been described in accordance with the provisionsof the patent statutes, it is to be understood that variouschanges inthe proportions and materials used may be made Without departing vfromthe spirit of the invention. It is desired, therefore, that the appendedclaims be given the broadest reasonable interpretation permissible inview of the prior art.

I claim as my invention:

1. Electrical contact means comprising a pair of separable contacts atleast one of which contains a conducting material and a substance whichgives off an arc extinguishing gas when acted on by an arc, and means ofinsulating material associated with said contact means for keeping thearcs drawn during separation of the' 'dered boric acid compressed into asolid composite mass, said contact containing from about 50% to 90% byweight of silver and from about 50% to 10% by weight of boric acid.

6. An electrical contact comprising an intl'- mate mixture of finelydivided silver and pow-I dered boric acid compressed into a solidcomposite mass, the boric acid content ranging from about 50% to 80% byweight.

7. An electrical contact comprising an intimate mixture of finelydivided graphite and pow dered boric acid compressed into a solidcomposite mass.-

8. An electrical contact comprising an intimate mixture of finelydivided graphite and powdered boric acid heated and compressed into asolid composite mass.

9. An electrical contact comprising an intimate mixture of finelydivided particles of graphite and powdered boric acid compressed into asolid composite mass, the boric acid content ranging from about 40% to50% by weight.

10. Electrical contact means comprising a pair of contacts which openand close in air, at least one of said contacts comprising a member ofconducting material having a number of capillary passages extendingtherethrough impregnated with a liquid which evolves an arcextinguishing fluid in the presence of an arc, said member beingdisposed in contact with a body of said liquid to maintain said passagesiilled with said liquid.

11. Electrical contact means comprising a pair of contacts which openand close in air, at least one of said contacts being composed of porousmetal having a large number of continuous lcapillary voids substantiallyuniformly distributed therethrough impregnated with a liquid whichevolves an arc extinguishing fluid when acted on by an arc forextinguishing arcs drawn by said contacts, said porous metal contactbeing disposed in absorbent relation with a body of said liquid tomaintain said voids filled with said liquid.

12. Electrical contact means comprising a pair of contacts which openand close in air, at least one of said contacts having a large number ofcapillary passages extending therethrough, said contact being disposedin absorbent relation with a body of liquid which evolves an arcextinguishing fluid when 'acted on by an arc.

13. Electrical contact means comprising a pair of contacts which openand close inv air, at least one of said contacts having a large numberof capillary passages extending therethrough filled with oil, saidcontact being disposed in absorbent relation With a body of oil tomaintain said passages lled with oil. j

14. Electrical contact means comprising a pair of contacts which openand close in air,l at least one of said contacts comprising a member ofconducting material having a large number of capillary passagesextending therethrough filled with an arc extingishing liquid, saidmember being disposed in contact with a body of said arc extinguishingliquid to maintain said passages filled with said liquid.

15. Electrical contact means comprising a pair of contacts which openand close in air, at least one of said contacts being composed of porousconducting material containing up to 40% voids forming a large number ofcontinuous capillary passages extending through the material of saidcontact, said contact being disposed in absorbent relation with a bodyof liquid which evolves an arc extinguishing fluid when acted on by anare to maintain Vsaid passages filled with said liquid to said contactto maintain said passages filled with said liquid.

17. An arc extinguishing electrical contact composed of an intimatemixture of finely divided particles of conducting material and finelydivided particles of a solid substance which evolves large quantities ofan arc extinguishing fiuid when acted on by an arc, said mixture beingcompressed into a solid composite mass.

1B. In a circuit interrupting device, a contact capable of emitting anarc extinguishing fiuid in the presence of an arc embedded in aninsulator also capable oi emitting an arc extinguishing duid 'in thepresence oi an arc, said insulator havinga portion disposed adjacent tbeface of said Contact so as to be acted on'by arcs drawn from saidcontact.

19. ln a circuit interrupting device, a contact member capable ofemitting a iluid in the presence oi an arc, and means providing atunnelshaped Wall at one end of said Contact member around the Contactace oi said member, said wall, being composed oi an insulating materialand capable oi emitting a uid when acted on by an arc.

2t. in a circuit interrupter, a contact member containing a non-fluidsubstance which emits a duid in the presence oi an arc, and meansproviding a funnel-shaped Wall at one end of said contact membersurrounding the face of said contact, said Wall being composed of aninsulating material and capable of emitting a fluid in the presence ofan arc.

2l. In a circuit interrupter, a contact member containing a materialwhich emits a uid in the presence of an arc, and an insulator providinga. funnel-shaped Wall about one end of said contact member, saidfunnel-shaped Wall being capable oi emitting a fluid in the presence ofan arc.

22. An electrical contact means comprising a pair o separable contactmembers disposed in fixed relation when in engagement with each other,at least one oi said Contact" members containing a non-gaseous substanceconfined in said Contact member which generates an are extinguishing gaswhen acted on by an arc for extinguisning arcs drawn between saidcontact members, and means providing a funnel-shaped Wall about one endof said Contact member.

JOSWPH SLETEIAN.

